Electrolyte

An electrolyte is a substance (usually a fluid) which has movable ions (electrically charged molecules or atoms) dissolved in it which make it electrically conductive, and which allow it to undergo electrolysis. An electrolyte may be a solution, a liquid compound or a solid.

Physics

Electrolytes contain mobile charges, hence they act as electrical conductors. The lifetime of free electrons in electrolytes is in the range of nanoseconds, so unlike metallic conductors, the moving charges in electrolytes are not negatively charged electrons, instead the polarity of is both positive and negative. During an electric current in an electrolyte, populations of opposite charges move through each other in opposite directions. Note that since the human body is an electrolytic conductor, during an electric shock, no electrons flow through body tissues.

Chemistry

Examples of electrolytes include acids and bases. The stronger the acid or base, the more electrolytic the substance will be. Salts are examples of strong electrolytes.

Physiology

In physiology, the main electrolytes are sodium, potassium, chlorine, bicarbonate and calcium. All higher lifeforms require a subtle electrolyte balance between the intracellular and extracellular milieu, as the small electrical potential thus created makes cells electrically exciteable, a feature of all cells but especially of nerve cells and muscle.

Electrolyte balance is maintained by oral intake and hormonal regulation, generally with the kidney as effector. In humans, salt homeostasis is regulated by such hormones as antidiuretic hormone, aldosterone and parathyroid hormone. Derangements of electrolyte balance often lead to cardiac and neurological complications, and most are medical emergencies. Specific electrolyte disturbances are hyper- and hyponatremia (excess and reduced sodium levels), hyper- and hypokalemia (potassium disturbances) and several rarer forms.

Measurement of electrolytes is a commonly performed diagnostic procedure, done as a blood test or as part of urinalysis. The interpretation of these values is quite meaningless outside the clinical history, and is often impossible without parallel measurement of renal function. Electrolytes measured first-line are sodium and potassium (chlorine is only important in specific cases, e.g. arterial blood gas interpretation).

Nutrition

Electrolyte drinks (containing salts of sodium and potassium, as well as carbohydrates) are used to replenish the body's fluid and salts levels after dehydration caused by exercise, heat stress, illness or drought. Giving water to a deydrated person is not the best way to restore fluid levels, because it dilutes the salts inside the body's cells and interferes with their chemical functions. This can lead to water intoxication. The drinks also help to replace the salts lost by sweating.

Sports drinks are electrolyte drinks with added carbohydrate, such as glucose, to provide energy. The drinks commonly sold to the public are isotonic (containing as near as possible the blood's natural concentration of sugars), with hypotonic (with a low level of sugar) and hypertonic (with a high level of carbohydrate) varieties available to athletes.

Electrolyte and sports drinks can be home-made by using the correct proportions of sugar, salt and water.

Electronics

Electrolytic conductors are used in electronic devices where the chemical action at a metal/electrolyte interface gives useful effects. In batteries the effect is used to store energy as chemical fuel on the surface of metal plates, and the electrolyte also serves as a conductor which connects the plates electrically. In some fuel cells a solid electrolyte or proton conductor connects the plates electrically while keeping the hydrogen and oxygen fuel gasses separated. In electroplating tanks, the electrolyte both deposits metal onto the object to be plated, and electrically connects that object in the circuit. In operation-hours gauges, two thin columns of mercury are separated by a small electrolyte-filled gap, and as charge is passed through the device, the metal dissolves on one side and plates out on the other, causing the visible gap to slowly move along. In electrolytic capacitors the chemical effect is used to produce an extremely thin 'dielectric' or insulating coating, while the electrolyte layer behaves as one capacitor plate. In some hygrometers the humidity of air is sensed by measuring the conductivity of a nearly dry electrolyte. Hot, softened glass is an electrolytic conductor, and some glass manufacturers keep the glass molten by passing a large electric current through it.